1. Field of the Invention
The invention relates to a grinding device, more particularly to a drill bit grinding device.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a commonly used drill bit 10 is shown to include a shank portion 11, a tip portion 13 opposite to the shank portion 11, and a body portion 12 between the shank and tip portions 11, 13. The tip portion 13 is formed with an apex 134, two cutting edges 133 defining a tip angle (A) (see FIG. 15) therebetween, two diametrically opposed lip portions 132, and two diametrically opposed flank portions 131, each of which is formed between a respective one of the cutting edges 133 and a respective one of the lip portions 132. The body portion 12 is formed with a pair of twisted flutes 121. Grinding swarfs are discharged via the flutes 121.
When the tip portion 13 of the drill bit 10 is worn out during the drilling operation, the apex 134 of the drill bit 10 becomes dull such that the drilling effect of the drill bit 10 is diminished and that resistance during a subsequent drilling operation is increased. As such, the flank and lip portions 131, 132 of the drill bit 10 have to be ground by a grinder (not shown) to sharpen the apex 134. However, the flank portions 131 are ground to form a sharpened tip angle (A) (see FIG. 15) based on a worker""s experience such that it is difficult to grind the drill bit 10 to form accurately a standardized tip angle (A) (see FIG. 15), e.g., at 90xc2x0, 118xc2x0, 150xc2x0, etc.
To overcome the above-mentioned drawbacks, many kinds of positioning devices for the drill bit 10 have been proposed heretofore, the main purpose of which is to position the drill bit 10 adjustably with respect to a grinding surface. However, control of the amount of the drill bit 10 to be ground is neglected by these devices. Furthermore, the structures of these positioning devices are somewhat complicated such that corresponding operations of holding and positioning the drill bit 10 are difficult to conduct. Moreover, since the flank and lip portions 131, 132 of the drill bit 10 have. to be ground individually, and since the angles between the axis of the drill bit 10 and. the surfaces of the flank portions 131 are different from those between the axis of the drill bit 10 and the surfaces of the lip portions 132, the position of the drill bit 10 has to be changed four times to complete the grinding operation. Each position change of the drill bit 10 includes the steps of unlocking and locking of the drill bit 10 with respect to a grinding seat (not shown), thereby resulting in a complex grinding operation.
Therefore, the main object of the present invention is to provide a drill bit grinding device that is easy to operate and that can measure the amount of the drill bit to be ground.
According to this invention, a grinding device includes a rotary grinding wheel having an annular grinding surface, a first grinding seat located in front of the grinding wheel, a sleeve disposed rotatably within a through hole in the first grinding seat, an abrasion measuring device for measuring amount of flank portions of a drill bit to be ground, and a tubular holding unit for holding releaseably the drill bit therein. The holding unit is sleeved on the drill bit, is disposed initially in the abrasion measuring device so as to fix position of the drill bit within the holding unit, and is then transferred into the first grinding seat for grinding the flank and lip portions of the drill bit.